The present invention is directed to heart valves, and specifically to mechanical heart valves. The present invention has particular applicability to bileaflet mechanical heart valves of the type disclosed in U.S. Pat. No. 4,535,483, issued to Klawitter et al on Aug. 20, 1985.
Heart valves are generally of two different types, biological and mechanical. Both offer advantages and disadvantages that are well known to those skilled in the art. One major concern with both types of heart valves is the wearing of critical components during the normal opening and closing of the valve. Mechanical heart valves experience wear from the opening and closing movement of the occluders. Further, the impact of the occluders against the valve body results in stress to the valve. Mechanical heart valves have also shown increased levels of hemolysis over tissue valves. However, due to the long term durability of mechanical hearts attempts have been made to reduce closing forces and associated stress and hemolysis.
Heart valves have been designed to reduce normal wear, and minimize the effects of the impact of the occluders against the valve body. For example, U.S. Pat. No. 4,443,894, issued to Klawitter on Apr. 24, 1984, discloses a heart valve having two occluders. Each occluder is formed with guides or protrusions which fit dog shaped depressions at opposite sides of the valve body. The occluders not only experience pivoting movement during the opening and closing of the heart valve, but experience a translation movement. The combination of the pivoting and translation movement of the occluder unloads strain applied to the occluder guides.
Other heart valve designs cushion the impact of the opening and closing of the valve by incorporating a rubber or silicone material in the valve sewing ring. The use of the rubber or silicone material in many of these heart valve designs was intended to provide a more compliant material for conforming to irregular tissue annuli, with the cushioning effect being accidental. For example ball poppet mechanical heart valves disclosed in U.S. Pat. No. 3,365,728, issued to Edwards et al on Jan. 30, 1968, U.S. Pat. No. 3,509,582, issued to Pierie et al on May 5, 1970, U.S. Pat. No. 3,534,410, issued to Raible on Oct. 20, 1970, and U.S. Pat. No. 3,723,996, issued to Raible et al on Apr. 3, 1973, provide for silicone rubber in the sewing ring. A tissue valve incorporating an elastic member in the sewing ring is disclosed in U.S. Pat. No. 4,680,031, issued to Alonso on July 14, 1987.
One particular type of mechanical heart valve is generally referred to as a bileaflet mechanical valve. This type of heart valve has demonstrated superior blood flow and a reduction in thromboembologic complications and blood hemolysis. One cause for the reduction of blood hemolysis is the use of pyrolytic carbon in forming the blood contacting portions of the heart valve. Pyrolytic carbon is blood compatible. However, pyrolytic carbon is a deformable, inelastic material which provides limited structural rigidity. An example of a pyrolytic carbon coated mechanical bileaflet heart valve is manufactured by St. Jude Medical, Inc. of Minneapolis, Minn. and disclosed under U.S. Pat. No. 4,078,268 issued to Possis and 4,276,658 issued to Hanson et al.
Some workers have suggested providing structural rigidity to the pyrolytic carbon heart valve body. One approach to providing this structural rigidity has been to incorporate a stiffener ring 25 about the pyrolytic carbon heart valve body to provide structural support. See U.S. Pat. No. 4,535,483, issued to Klawitter et al. The stiffening ring is situated about the exterior surface of the heart valve body in close proximity to the retainer ring of the sewing ring. The retainer function to maintain the sewing ring about the heart valve body. The disclosed heart valve design also incorporates a "resilient polymeric filler ring 76". formed of low density or foam polytetrafluoroethylene in the sewing ring.
The Klawitter et al bileaflet heart valves provide for the advantages of bileaflet heart valves while also providing structural rigidity through the use of the stiffening ring. The use of the "filler ring 76", which has primarily been utilized in heart valves positioned at the mitral valve location provides a degree of cushioning of the impact of the occluders against the valve body during closing.
While the Klawitter et al heart valves provide numerous advantages over previously available heart valves, both mechanical and tissue, recent investigations have shown the continued presence of the stress effects associated with the opening and closing of the valve occluders. It would thus be desirable to provide for a modification of bileaflet heart valves having a pyrolytic carbon valve body incorporating a stiffening ring which further reduces the stress effects from the opening and closing of the valve occluders.